Dr. Roach: The magic of math in assessing risk
Dear Dr. Roach: In a recent column, you reported using “the standard risk calculator” to determine that a person has a risk of heart attack or stroke in the next 10 years of “6.8%.” What exactly does this mean? How was the risk determined? How does such a risk calculation compare with “number needed to treat,” the number of persons who must be treated to benefit one person in the group?
Dear T. A.: A risk calculator takes important characteristics about a person and estimates the possibility that an event — i.e., heart attack or stroke — will happen. In the column you mention, the American Heart Association and American College of Cardiology looked at data from tens of thousands of people and used a person’s age, gender, race, total and HDL cholesterol, blood pressure (and whether it is treated), presence or absence of diabetes, and smoking history to estimate the likelihood of that person having a heart attack or stroke in the next 10 years. It is not appropriate for a person with a known history of heart disease or stroke. The person who wrote to me had a fairly low value, and this calculator is used to provide information that helps the person and their doctor decide what treatments are appropriate.
The calculator isn’t perfect. It does not take into account many other important risk factors, such as family history, quality of diet, how much a person exercises, and other risk factors like rheumatoid arthritis. Nonetheless, it’s a good place to start a conversation.
In order to calculate a number needed to treat, you need to know how the risk would be affected by that treatment. For example, a person with a 10% risk might decrease their risk to about 8% by taking a statin drug. Although drug companies advertise this as a 20% reduction in risk, I think a person gets more information by stating that it’s a 2% absolute reduction.
The number needed to treat is just 100% divided by the absolute risk reduction. In this case, 50 people would need to be treated with the statin for 10 years to prevent one person from having a heart attack or stroke. The higher the absolute risk and the better the intervention, the larger the absolute benefit and the fewer people needed to be treated. Some calculators will give the estimated absolute risk reduction from treatment.
For a person who really wants to know whether a treatment is worth it, understanding the benefit meaningfully is critical.
An upcoming column will discuss possible bias in this calculator.
Dear Dr. Roach: My son was diagnosed with breast cancer. He just turned 51. I was wondering how many men have breast cancer. He is a wonderful person and well-liked. Why did it happen to him?
Dear M.O.: One percent or less of breast cancer is in men, and the vast majority of men have no identifiable risk. I am sorry your son has this diagnosis, and wish him well with treatment.
Men often seek medical attention for a breast mass later than women, due to lack of knowledge about this condition as well as lack of screening. Men typically get breast cancer at older ages than women, but treatment is similar, with surgery, sometimes radiation and/or chemotherapy, guided by the results and hormone status of the breast tumor pathology.
Men with breast cancer are at high risk for certain genetic conditions, including the BRCA gene mutations. He should consider genetic testing and the impact that might have on his children, if any. It would also affect screening for other conditions.
Readers may email questions to ToYourGoodHealth@med.cornell.edu.